Evaluation of fabrication process for a novel Chip-to-Wafer (C2W) 3D integration approach using an alignment template

We proposed a novel Chip-to-Wafer (C2W) 3D integration approach using an alignment template and well-controlled wafer-level bonding. With an alignment template as position reference, this approach can align all the top chips to the template corners and bond them to the host wafer simultaneously, resulting in high throughput, few thermal cycles, precise alignment accuracy, and independence of commercial alignment tools. In this paper, several evaluation methods are used to further study the feasibility of this C2W 3D approach: unit fabrication processes are inspected by optical and/or surface profiler, chip edge and template sidewall definition is examined by scanning electron microscope (SEM), stress evaluation is conducted based on wafer bow monitoring, alignment accuracy is checked through infrared (IR) imaging system, finally thermal reliability for bonded chip/wafer pairs is tested. Optimized fabrication process with improved chip-to-wafer alignment and bonding results are presented. Different designs of alignment template and their effects on alignment accuracy and wafer bow are also compared.